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Waters, J.; Garrigan, J. T. Water Res. 1983,17,1549-1562. Hon-nami, H.; Hanya, T. J. Chromatogr. 1978,161,205-212. Parsons, J. S. J . Gas Chromatogr. 1967, 5, 254-256. Watanabe, S.; Nukiyama, M.; Takagi, F.; Iida, K.; Kaise, T.; Wada, Y. J . Food Hyg. SOC.Jpn. 1975, 16, 212-217. Kirkland, J. J. Anal. Chem. 1960,32, 1389-1393. Imaida, M.; Sumimoto, T.; Yada, M.; Yoshida, M.; Koyama, K.; Kunita, N. J. Food Hyg. SOC.Jpn. 1975,16,218-224. Grob, K.; Grob, G.; Blum, W.; Walther, W. J. Chromatogr. 1982,244, 197-208. Eganhouse, R. P.; Blumfield, D. L.; Kaplan, I. R. Environ. Sci. Technol. 1983, 17, 523-530. Lester, J. N. In “Environmental Effects of Organic and Inorganic Contaminants in Sewage Sludge”; Davis, R. D., Hucker, G., L’Hermite, P., Eds.; Reidel: Dordrecht, Holland, 1983; pp 3-18. McLeese, D. W.; Zitko, W.; Sergeant, D. B.; Burridge, L.; Metcalfe, C. D. Chemosphere 1981, 10, 723-730. Bringman, G.; Kuhn, R. Z. Wasser Abwasser Forsch. 1982, 15, 1-6. Divo, C.; Cardini, G. Tenside Deterg. 1980, 17, 30-36. Gledhill, W. E. Appl. Microbiol. 1975, 30, 922-929. Swisher, R. D. Tenside Deterg. 1981, 18, 57-63.
a-Dicarbonyl Yields from the NO,-Air Aromatic Hydrocarbons in Air
Leidner, H.; Gloor, R.; Wuest, D.; Wuhrmann, K. Xenobiotica 1980, 10, 47-56. Pitter, P.; Fuka, T. Tenside Deterg. 1979, 16, 298-302. Wuhrmann, K.; Mechsner, K. EAWAG News 1974,3,1-2. Inoue, K.; Kaneko, K.; Yoshida, M. Soil Sci. Plant Nutr. (Tokyo) 1978,24,91-102. Schaumberg, G. D.; LeVesque-Madore, C. S.; Sposito, G.; Lund, L. J. J . Environ. Qual. 1980, 9, 297-303. Huddleston, R. L.; Allred, R. C. Dev. Ind. Microbiol. 1963, 4, 24-38. Wayman, G. H. In “Proceedings of the International Clay Conference”; Rosenquist, I. T., Ed.; Stockholm, 1963; pp 329-342, Vol. 1. Motschi, H.; McEvoy, J. Naturwissenschaften 1985, 72, 654-655. McEvoy, J.; Giger, W. Naturwissenschaften 1985, 72, 429-431.
Received for review April 8, 1985. Accepted Septemter 3, 1985. This project was mainly funded by the Swiss National Science Foundation (Nationales Forschungsprogramm 70: “Organic Contaminants in Sewage Sludges”).
Photooxidations of a Series of
Ernest0 C. Tuazon,” Hdline Mac Leod, Roger Atkinson, and William P. L. Carter Statewide Air Pollution Research Center, University of California, Riverside, California 9252 1
The yields of the ring cleavage products glyoxal, methylglyoxal, and biacetyl from the reactions of OH radicals with benzene, toluene, o-, m-, and p-xylene, and 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene in the presence of parts per million concentrations of NO have been determined in 1atm of air at 298 f 2 K using in situ long-path-length Fourier transform infrared absorption spectroscopy and differential optical absorption spectroscopy with supplementary gas chromatographic analyses. The yields of glyoxal and methylglyoxal, after correction for their photolysis and reaction with OH radicals, were, respectively, as follows: from toluene, 0.105 f 0.019 and 0.146 f 0.006; from o-xylene, 0.087 f 0.012 and 0.246 f 0.020; from m-xylene, 0.086 f 0.011 and 0.319 f 0.009; from p-xylene, 0.225 f 0.039 and 0.105 f 0.034; from 1,2,3-trimethylbenzene, 0.058 f 0.008 and 0.152 f 0.025; and from 1,2,4-trimethylbenzene, 0.048 f 0.005 and 0.357 f 0.017. In addition, a glyoxal yield from benzene of 0.207 f 0.019, a methylglyoxal yield from 1,3,5-trimethylbenzeneof 0.602 f 0.033, and biacetyl yields from 1,2,3- and 1,2,4-trimethylbenzene of 0.316 f 0.036 and 0.048 f 0.009, respectively, were determined. These data are important inputs to chemical models of the NO,-air photooxidations of these aromatic hydrocarbons.
Introduction Aromatic hydrocarbons are important constituents of commercial fuels (1-3) and of emissions from mobile sources ( 1 , 3 ) . However, despite numerous experimental and computer modeling studies, the reaction pathways occurring during their atmospheric photooxidations are still not well-understood (4-9). Kinetic and environmental chamber studies have shown that under atmospheric conditions the sole loss process of the aromatic hydrocarbons is due to reaction with the hydroxyl radical (7, 9-12). These OH radical reactions 0013-936X/86/0920-0383$01.50/0
have been shown to proceed via two pathways, namely H atom abstraction from the substituent alkyl groups and OH radical addition to the aromatic ring (7, 9-12), as illustrated in eq 1 and 2 for toluene.
A
The H-atom abstraction route is relatively minor, accounting for -8% of the overall reaction for toluene (12, 13) and -2-9% for the xylenes and trimethylbenzenes (12). While the subsequent chemistry of the benzyl and substituted benzyl radicals appears to be adequately understood ( 7 , 9 , l o ) , many uncertainties remain concerning the subsequent chemistry of the OH-aromatic adducts (A) under atmospheric conditions (7-9, 12). Reaction of the OH-aromatic adducts (i.e., hydroxycyclohexadienyl or methyl-substituted hydroxycyclohexadienyl radicals) with O2 is expected to lead to the formation of hydroxyaromatics (7, 10, 12). Indeed the cresol isomers are formed from toluene in -16% yield (13), with o-cresol being the dominant isomer (14). However, the observation of the a-dicarbonyls glyoxal, methylglyoxal, and biacetyl in significant yields from the methyl-substituted aromatic hydrocarbons (8, 13, 15-19) and of a variety of other acyclic oxygenated products from toluene (5, 6, 20), o-xylene ( 5 ) , and 1,2,4-trimethylbenzene (21)
0 1986 American Chemical Society
Environ. Sci. Technol., Vol. 20, No. 4, 1986
383
shows that ring cleavage is also an important overall reaction pathway. In this work, in an extension of our recent investigation of the glyoxal and methylglyoxal yields from toluene and m- and p-xylene (8),we have used long-path-length Fourier transform infrared (FT-IR) absorption spectroscopy, long-path-length differential optical absorption spectroscopy (DOAS), and gas chromatography (GC) to determine the yields of the a-dicarbonyls glyoxal, methylglyoxal, and biacetyl from the NO,-air photooxidations of benzene, toluene, the xylene isomers, and the trimethylbenzene isomers at -740 torr total pressure of air and 298 f 2 K.
Experimental Section The experimental techniques used were essentially identical to those described previously (8). NO,-air photooxidations of the aromatic hydrocarbons were carried out in the SAPRC 5800-L evacuable, Teflon-coated environmental chamber, with radiation being provided by a 25-kW xenon arc (22). This environmental chamber is equipped with two sets of multiple-reflection White-type optical systems. One set, on a diametrical axis with a base path of 1.30 m, was interfaced to a Nicolet FT-IR spectrometer. The second set, on a longitudinal axis with a base path of 3.77 m, was interfaced to a differential optical absorption spectrometer. As in our previous study (8), DOAS measurements of glyoxal were carried out using path lengths from 45.2 to 150.8 m, utilizing the wavelength region 430-460 nm. The optimum detection sensitivity for glyoxal was -3 x 1011 molecule cm-3 for the maximum path length used (150.8 m). Due to the much weaker spectral features of methylglyoxal (for which the detection sensitivity was -5 x 10l2molecule cm-3 at 150 m) its unambiguous detection and measurement by DOAS during these experiments could not be carried out, particularly in the presence of interfering NO, absorption bands. Glyoxal, methylglyoxal, and the aromatic hydrocarbons were monitored by FT-IR absorption spectroscopy simultaneously with the DOAS measurements of glyoxal. For the FT-IR measurements, a path length of 62.9 m was routinely used with a spectral resolution (unapodized) of 1cm-'. Spectra were recorded by utilizing both a liquidN2-cooled HgCdTe detector (600-2000 cm-l) and a liquid-N,-cooled InSb detector (2000-4000 cm-I). Quantitative analysis was carried out by linear subtraction of a spectrum's absorption bands with the use of calibrated reference spectra of the authentic sample. For the aromatic hydrocarbons the subtraction procedure employed their characteristic absorption bands in both the regions 650-850 cm-I and 2850-3100 cm-l. Glyoxal and methylglyoxal were monitored at their absorptions centered, respectively, a t -2835 and 2829 cm-l. The first step in the analysis of these superimposed absorption bands was the subtraction of the more highly structured band of glyoxal, as verified by the DOAS data, followed by the determination of the residual absorption of methylglyoxal. FT-IR detection sensitivities for glyoxal and methylglyoxal were similar, being -4 X 10l2molecule cm-3 at the path length and resolution employed. Biacetyl was analyzed by gas chromatography with electron capture detection, using a 18 in X 0.25 in. Teflon column of 5% Carbowax 400 on Chromosorb G (80/100 mesh) a t 300 K. The detector response was calibrated periodically during this study, and gas samples were diluted as necessary to utilize the linear portion of the calibration curve. Hydroxyl radicals were generated by the photolysis of methyl nitrite in air a t wavelengths 2300 nm (7) 384
Environ. Sci. Technol., Vol. 20, No. 4, 1986
-
CHSONO + hv CH30 + 0, HO2
+ NO
CH30
HCHO
-+
OH
+ NO
+ HOz
+ NO2
NO was included in the reaction mixtures in order to minimize the formation of O3 and NO3 radicals. The initial concentrations of the CH30NO-NO-aromatic hydrocarbon-air mixtures were CH30N0, -2.4 X 1014molecule ~ m - NO, ~ ; -1.2 X lOI4 molecule ~ m - aromatic ~; hydrocarbon, (2.5-5) X lOI4 molecule ~ m - with ~ ; approximately 1atm of synthetic air (80% N2 + 20% 0,) as the diluent gas. Each experiment consisted of cumulative, short-period (3-10-min) irradiations, with total irradiation times up to 60 min. DOAS and FT-IR spectra were recorded, and GC samples were taken, between these irradiation periods. This procedure minimized the effect of stray radiation on the DOAS instrument and ensured that all the analyses corresponded to the same extent of reaction. The light intensity in these experiments, as determined from an irradiation of a biacetyl-air mixture, corresponded to a biacetyl photolysis rate of 1.25 X s-l.
-
Results CH30NO-NO-air irradiations of benzene, toluene, 0-, m-, and p-xylene, and 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene were carried out at 298 K and -740 torr total pressure of air, with two or three separate experiments being carried out for all but m-xylene. The concentrations of the aromatic hydrocarbons, glyoxal, methylglyoxal, and biacetyl as analyzed by FT-IR, DOAS, and GC techniques are given in Tables 11-IX. (Tables 11-IX are available as supplementary material for this manuscript; see paragraph a t end of text regarding supplementary material). The observed a-dicarbonyl yields had to be corrected for reaction with OH radicals and photolysis (8) in order to derive the formation yields of these compounds. The reaction sequence is OH
+ aromatic
- -NO, 0,
+ a-dicarbonyl a-dicarbonyl + hv .-,
OH
Y a-dicarbonyl
(3)
products
(4)
products
(5)
where reaction 3 is complex (8) and Y is the formation yield of the individual a-dicarbonyls from the aromatic hydrocarbon studied. By making the reasonable assumption that the OH radical concentrations were essentially constant over the small irradiation periods, then (8) [aromatic] tz = [aromatic]tle-k3[0H1(t2-tl)
(1)
and [a-dicarbonyl],, = [a-di~arbonyl]~,e-(~~[~~]+~~)(~~~~~) + Yt,~t,[aromaticltlk3[0Hl [e-k~(OHl(t2-td - e-(kdOHI + ks)(tz-td]
[(h- kJ[OHI + k5l
(11)
where [aromatic]t l , [a-dicarbonyl]t l and [aromatic]t 2 , [adicarbonyl],, are the aromatic hydrocarbon and a-dicarbonyl concentrations observed at times tl and t 2 , respectively, and Ytl+is the formation yield of the individual a-dicarbonyls over the time period tl-t2. Computer calculations showed that eq I1 yielded negligible (
